In Wrath of the Lich King Classic hunter pets benefit from 'pet scaling'. This just means that your pet gets to add some of your stats to their own stats, so that their power scales with your power. The basics are very simple:
Pets get about 45% of their hunter's stamina added to their stamina.
Pets get about 35% of their hunter's armor added to their armor.
Pets get about 22% of their hunter's ranged attack power added to their melee attack power.
Pets get about 12.5% of their hunter's ranged attack power added to their spell damage.
Pets get about 40% of their hunter's resistances added to their own resistances.
Pets inherit their hunter's hit and critical rates.